Viewing.ppt

Viewing (I) Outline Classical and Computer Viewing Viewing with a Computer Positioning of the Camera Simple Projections Projections in OpenGL Classical and Computer Viewing Classical Viewing Orthographic Projections Axonometric Projections Oblique Projections Perspective Viewing Synthetic-camera Model The projectors meet at the centre of projection (COP). The COP corresponds to the center of the lens in the camera or in the eye. It is the origin of the camera frame in graphics systems. The projection surface is a plane. The projectors are straight lines, based on geometric optics. The class of projections is also called planar geometric projections. As the COP is moved to infinity, the projectors become parallel and the COP can be replaced by a direction of projection (DOP). Views with a finite COP are called perspective views. Views with a COP at infinity is called parallel views. Computer graphics systems have two fundamental types of viewing (parallel and perspective). Classical graphics appears to permit a host of different views. Classical viewing intends to show a specific relationship among an object, the viewer and the projection plane. Computer graphics systems prefers complete independence of all specifications. Classical Viewing Orthographic Projections Axonometric Projection 轴测投影 Oblique Projections Viewing with a Computer Viewing consists of two fundamental operations. 1st we must position the camera. This is the job of the model-view transformations, After vertices pass through this transformation, they are in the camera frame. 2nd step is the application of the projection transformation. It applies the specified projection – orthographic or perspective – to the vertices and puts objects within the specified clipping volume in a normalized clipping volume. Positioning of the Camera Our starting point is the world frame. We describe the camera’s position and orientation in this frame. The precise type of image that we wish to obtain – perspective